A device and method for accurately measuring pressure inside a high pressure chamber at high temperatures

Abstract

The application provides a device and method for accurately measuring the pressure in a high-pressure cavity at high temperature, comprising the following steps: setting the temperature range and pressure range of measurement; selecting at least two kinds of metal as calibration elements of a pressure sensor, and making the metal into a wire resistor to determine the melting temperature of the calibration elements; introducing a plurality of insulated electrical contacts into a synthetic cavity of a high-pressure device, and connecting the insulated electrical contacts with the calibration elements and thermocouples respectively; placing the hot end of the thermocouples close to the position of the calibration elements of the pressure sensor; connecting the at least two wire resistors on the pressure sensor in parallel, and placing the wire resistors in the quasi-stationary water medium of the synthetic cavity of the high-pressure device; determining the melting temperature when the calibration elements are fused, determining the pressure when the calibration elements are fused, and establishing the functional relationship between the pressure and the temperature in the synthetic cavity by fitting; and determining the pressure of the quasi-stationary water medium in the synthetic cavity at the corresponding temperature by the functional relationship. The application realizes accurate pressure measurement of the synthetic cavity at high temperature.

Description

Technical Field

[0001] This invention relates to the technical field of high pressure measurement, and in particular to a device and method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures. Background Technology

[0002] The challenge of accurately measuring pressure in high-pressure devices, especially under conditions of quasi-static water pressure transmission and heating, is particularly prominent for six-sided triaxial compression presses. These presses can achieve compression of ultra-large working volumes of 27-1000 dm³, with reaction unit volumes ranging from 0.5 to 100 dm³. Therefore, inaccurate pressure settings as process parameters can lead to significant losses due to suboptimal product yield and reduced durability of the carbide components used to achieve ultra-high pressure compression of 1-20 GPa.

[0003] Besides the lack of pressure control, the relationship between the compression efficiency of a compression vessel and the shape of the compressible gasket and the configuration of the cemented carbide indenter, factors crucial for achieving maximum pressure within the compression chamber, cannot currently be assessed. For example, in the crystal growth of polycrystalline diamond and cubic boron nitride cutting discs, such control is essential to ensure the highest sample density. This problem significantly limits the application of these materials in modern high-tech fields, such as high-hardness ceramic machining, drilling tools, and heat sinks and thermal conductive elements in the electronics industry.

[0004] To generate high pressures of 2–3 GPa or higher and apply them as process parameters for production purposes, such as the growth of diamond samples, diamond single crystals, and cubic boron nitride single crystals, high-pressure devices operating with quasi-hydrostatic pressure-transmitting media are typically employed. Due to the low internal friction coefficient and high plasticity of these media, material compression at pressures of 10 GPa or even higher can be achieved.

[0005] A key challenge in operating high-pressure devices using quasi-static water pressure-transmitting media is measuring the high pressure within the reaction unit, i.e., the synthesis chamber. This problem is typically solved by establishing the loading characteristic curves of the high-pressure device. The loading characteristics of the high-pressure device are experimentally determined, reflecting a functional relationship between the compressive pressure changes of the quasi-static water medium. For different types of existing high-pressure devices, such as Belt, Toroid, BARS, and various multi-head device modifications, establishing their loading characteristics allows for the determination of permissible compressive force limits, maximizing their use for research and industrial production purposes.

[0006] Currently, these loading characteristics are only measured at room temperature. However, in actual production, heating the reaction unit in the high-pressure unit significantly alters the pressure value determined based on the room-temperature loading characteristics. Due to the thermal expansion of the components of the high-pressure unit, the pressure in the reaction unit increases during heating. According to expert assessments, this factor can cause the pressure in the working chamber of the high-pressure unit to increase by 2–4 GPa, or even reach 50% of the initial maximum pressure value determined at room temperature, when operating within a pressure range of 3–10 GPa and a temperature range of 500–2000 °C.

[0007] When determining pressure using loading characteristics under high-pressure heating conditions, another source of pressure measurement error is the phase transition process of the container material, which involves a decrease in volume. In this case, the initial pressure may decrease. Depending on the amount of phase transition material in the synthesis chamber that causes the pressure decrease, this pressure reduction can reach 10% or even higher.

[0008] The loading characteristics used to establish the relationship between pressure and container compressibility are determined using sensors that measure changes in the resistance of a reference substance and material (called calibration elements). In these calibration elements, the resistance changes abruptly when the pressure reaches a fixed value due to a first-order phase transition (change in crystal structure or melting).

[0009] These sensors typically consist of a metal reference element (wire-like) or a sheet reference element (semiconductor reference element), connected to lead-out electrical contacts, through which they are connected to the measurement circuit. A schematic diagram illustrating the principle of a resistance sensor connected to the measurement circuit for measuring the resistance of the reference element during high-voltage device loading is shown below. Figure 1 The measurement circuit includes a power supply 1, a variable resistor 2 for setting the operating current value through the pressure sensor, a pressure sensor (calibration element) 13 made of a reference material, and a measuring device 3 for determining the thermoelectric potential and pressure phase transition point, connected in series.

[0010] The pressure reference points used to establish the loading characteristics of the high-pressure device were determined at room temperature using a specialized method and high-precision high-pressure equipment. In the pressure range below 10 GPa, bismuth (Bi) was the primary metallic reference material, with the Bi I–Bi II and Bi III–Bi IV phase transitions corresponding to known reference pressure points of 2.56 ± 0.1 GPa and 7.7 ± 0.3 GPa (room temperature, RT), respectively. In addition, tantalum (Ta) (3.67 ± 0.3 GPa, RT), barium (Ba) (5.5 ± 1 GPa, RT), and tin (Sn) (9.4 ± 0.4 GPa, RT) were also used as calibration elements.

[0011] Using the data from fixed pressure points on the aforementioned metallic reference material, the loading characteristics of a known high-pressure device under quasi-static compression and room temperature conditions can be determined. The form of the loading characteristics depends on the ability of the high-pressure device in its specific structure to compress the material within the high-pressure chamber through seal deformation. The loading characteristics typically consist of two segments, the first being a linear segment resulting from a uniform reduction in seal thickness, characterized by… , The displacement x of the indenter remains constant relative to the applied force F. As the compressive force increases, the surface and internal friction of the compressible gasket material increases, leading to… As the value decreases, the loading characteristics gradually exhibit a curved parabolic shape, rather than symmetrically approaching the final value determined by the strength limit of the hard alloy indenter of the compression deformation shim.

[0012] The loading process of the domestically produced six-sided high-pressure device consists of two stages, each corresponding to different compression force application rates and different temperature conditions, under which the compressible gasket deforms. The two-stage loading cycle of this cubic press results in a significant difference between the actual pressure value reached in its working chamber and the pressure value determined based on room temperature loading characteristics. This combined two-stage compression cycle can significantly improve the quality indicators of the ultra-high pressure formation process, as follows: Typically, the first stage of loading refers to increasing the pressure to 70–80% of the preset maximum value; subsequently, the second stage of compression begins under the condition of activating the working volume heating. At this time, the pressure rise rate in the press system is selected to be significantly lower than the pressure rise rate in the first stage process, ensuring that the compressible gasket is heated to a temperature 30–40 °C higher than the initial temperature.

[0013] As temperatures rise, compressible gaskets become more ductile and more prone to deformation. This facilitates the reduction of compressible gasket material... The numerical values ​​are used to improve the compression efficiency of the working volume. At the same time, the length of the linear section of the loading characteristic is increased, the upper limit of the pressure reached is increased, and the working stability of the high-pressure device is also improved.

[0014] The overall analysis shows that in order to optimize the process of achieving the maximum pressure in the working chamber when using a combined two-stage loading cycle in a six-sided top press, it is necessary to determine the relationship between the following parameters: the ratio of the loading duration of the first stage and the second stage, the temperature and its heating rate when heating the high-pressure device, and the pressure value reached during the compression of the working medium in the second stage.

[0015] However, due to the current lack of methods for measuring the pressure within a hydrostatic high-pressure device under high-temperature conditions, it is impossible to determine and optimize the relationship between the aforementioned parameters. Furthermore, it should be noted that current methods for establishing load characteristics under high-temperature conditions are extremely demanding, as it requires determining the structural form of the pressure-bearing end of the carbide indenter to ensure the required pressure distribution within the reaction volume of the high-pressure device, and achieving the maximum pressure value by altering its shape—primarily the ratio between the size of the pressure-bearing area and the inclination angle of the pressure-bearing surface. Summary of the Invention

[0016] To address the technical problem that existing technologies cannot measure pressure under high-temperature conditions, this invention proposes a device and method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures. This device is used to determine pressure changes and establish the compression loading characteristics of a quasi-static medium in a high-pressure device that operates using the compressible gasket densification principle. By establishing loading characteristic curves under pressure conditions of 1–10 GPa and temperature conditions of 500–2000℃, the quasi-static pressure in the high-pressure device can be evaluated. This invention is particularly suitable for six-sided top presses.

[0017] To achieve the above objectives, the technical solution of the present invention is as follows: A method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures, comprising the following steps:

[0018] Step 1. Set the temperature and pressure ranges for measurement;

[0019] Step 2. Select at least two metals as calibration elements for the pressure sensor and fabricate them into wire resistors. Determine the melting temperature of the calibration elements based on their temperature-pressure curves.

[0020] Step 3. Introduce multiple insulating electrical contacts into the synthesis chamber of the high-voltage device. The insulating electrical contacts are connected to the calibration element and the thermocouple, respectively.

[0021] Step 4. Bring the hot junction of the thermocouple close to the calibration element of the pressure sensor;

[0022] Step 5. At least two wire resistors on the pressure sensor are connected in parallel and placed in the quasi-static water medium of the synthesis chamber of the high-pressure device;

[0023] Step 6. Based on the melting temperature of the calibration element when it melts, determine the pressure of the calibration element when it melts using the temperature-pressure curve of the calibration element, and establish a functional relationship between the pressure and temperature inside the synthesis chamber by fitting; determine the pressure of the quasi-static medium inside the synthesis chamber at the corresponding temperature through the functional relationship.

[0024] Preferably, the temperature range is 500–2000℃ and the pressure range is 1–10 GPa; within the synthesis chamber of the high-pressure device, the current jump is recorded when each calibration element melts, and the corresponding melting temperature T is determined. 熔 The pressure at which melting occurs is determined based on the temperature-pressure curve of the calibration element; the melting temperature T is measured using at least two calibration elements. 熔 The corresponding pressure was fitted to establish the functional relationship between the internal pressure and temperature of the synthesis chamber.

[0025] Preferably, the metal is at least two of the following: Cd, Pb, Al, Ag, Cu, Au, Ni, Fe, Pd, Pt, Ge, and Si.

[0026] For a temperature range of 500–1400℃, the phase temperatures and pressures of Cd, Pb, Ge, Si, Al, Ag, Au, and Cu are used to determine the temperature-pressure curves in step 2;

[0027] When the temperature is greater than 1400–1500℃, the pressure of the quasi-static medium is measured using a parallel wire resistor made of at least two of Fe, Ni, Pd or Pt.

[0028] Preferably, the filament resistor has a cross-sectional area of ​​0.7–0.8 mm² and a length of 3–5 mm;

[0029] The distance between the hot junction of the thermocouple and the calibration element is 0.2 mm to 2.5 mm;

[0030] At least two calibration elements are arranged in the same plane and isolated from the plane containing the hot junction of the thermocouple by an insulating layer.

[0031] Preferably, the method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 4 is characterized in that the number of insulating electrical contacts is provided in multiple ways, including insulating electrical contacts for heating the filament resistor, insulating electrical contacts for measuring the temperature by measuring the thermoelectric potential of the thermocouple, and insulating electrical contacts for determining the melting process of the calibration element from solid to liquid; the leads of the multiple insulating electrical contacts are connected by a hard alloy pressing anvil.

[0032] The thermocouple is a Pt-PtRh thermocouple, which is directly introduced into the working volume of the synthesis chamber of the high-pressure device.

[0033] Preferably, the signal change on the filament resistor is caused by a change in geometry and a dissipation during the melting process, which causes the circuit to break and the operating current to stop flowing.

[0034] When melting occurs under quasi-hydrostatic compression conditions in NaCl or CsCl plastic media, the melting temperature T corresponding to each calibration element is reached. 熔 When this happens, the filament resistor loses its original shape and spreads out in the form of droplets with a diameter of 0.1–0.5 mm.

[0035] A device for accurately measuring the internal pressure of a high-pressure cavity at high temperatures includes a synthesis block, an insulation tube inside the synthesis block, a conductive graphite tube inside the insulation tube, and conductive graphite sheets at both ends of the conductive graphite tube; the conductive graphite tube is a synthesis cavity filled with a quasi-static water medium, and a pressure sensor is installed in the placement area in the middle of the synthesis cavity.

[0036] The pressure sensor includes a housing with two symmetrical electrical contact graphite sheets on the housing and two parallel calibration elements between the two electrical contact graphite sheets.

[0037] Preferably, the housing has two symmetrically distributed holes, each hole having an electrical contact graphite sheet. The two electrical contact graphite sheets are connected by at least two parallel calibration elements. The electrical contact graphite sheets have calibration element signal wires. The lower part of the housing is in contact with a thermocouple junction, which is connected to a thermocouple signal wire. The calibration element signal wire and the thermocouple signal wire are in contact with the working surface of a hard alloy pressure anvil.

[0038] Preferably, the conductive graphite sheet has stone pillars for pressure transmission at both ends, and a steel cap for conducting electricity is provided on the outside of the stone pillar. The steel cap is sealed to the composite block through a stone ring.

[0039] The minimum distance between the thermocouple (12) and the calibration element is 0.2-0.35 mm.

[0040] Preferably, the quasi-static medium is hexagonal boron nitride (h-BN);

[0041] The shell is disc-shaped;

[0042] At least two of the calibration elements have corresponding contact terminals disposed on an electrical contact graphite sheet, and the calibration element signal wires are electrically connected to the center of the electrical contact graphite sheet;

[0043] The thermocouple junction is located at the center of the lower part of the housing and between the calibrations (13).

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows: By constructing a measuring device at high temperature and developing a corresponding measuring method, this application realizes accurate pressure measurement of the synthetic cavity at high temperature, breaking through the bottleneck of large deviation and difficulty in guiding production in the existing methods. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the circuit connection for a pressure sensor used to measure changes in the resistance of a reference material.

[0047] Figure 2 These are melting curves for various metals and semiconductors.

[0048] Figure 3 Circuit diagram for connecting calibration elements with different melting temperatures to a DC power supply.

[0049] Figure 4 This is a schematic diagram of the assembly of the high-pressure device used for the operation of the pressure sensor according to the present invention.

[0050] Figure 5 This is a schematic diagram of the pressure sensor of the present invention.

[0051] Figure 6 for Figure 5 View from AA.

[0052] Figure 7 for Figure 5 BB view.

[0053] Figure 8 The loading characteristic curve is for a press with a plunger diameter of 420 mm.

[0054] Figure 9 This is a schematic diagram of the recording results of the melting effect of the pressure sensor, where a is a pressure sensor with two resistive elements (Ag-Cu) and b is a pressure sensor with three resistive elements (Al-Ag-Cu).

[0055] In the diagram, 1 is the composite block, 2 is the stone ring, 3 is the steel cap, 4 is the stone pillar, 5 is the conductive graphite sheet, 6 is the conductive graphite tube, 7 is the insulation tube, 8 is the sensor placement area, 9 is the composite cavity, 11 is the housing, 12 is the thermocouple contact, 13 is the calibration element, 14 is the electrical contact graphite sheet, 15 is the calibration element signal wire, 16 is the thermocouple signal wire, 21 is the external power supply, 22 is the rheostat, and 23 is the measuring device. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Example 1

[0058] A method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures includes the following steps:

[0059] Step 1. Set the temperature and pressure ranges for measurement.

[0060] Under conditions of temperature T = 500–2000 ℃ and pressure p = 1–10 GPa, the high pressure value in the quasi-static high-pressure device can be measured, covering the operation of most sensors. The principle of high pressure value measurement in the quasi-static high-pressure device is based on the unique correspondence between pressure p and temperature T during solid melting. The functional relationship between melting temperature and pressure is: T 熔 =f(p), whose parameters have been predetermined with high precision through experiments and / or experimental-computation methods and published in scientific literature; by measuring the melting temperature T 熔 This allows us to determine the corresponding pressure value in a quasi-static medium.

[0061] Step 2. Select various metals as calibration elements for the pressure sensor and fabricate them into wire resistors. Determine the melting temperature of the calibration elements based on their temperature-pressure curves.

[0062] To achieve the objectives of this invention, and using the method described in point 1, 12 elements were selected, including 10 metals and 2 semiconductors—Cd, Pb, Al, Ag, Cu, Au, Ni, Fe, Pd, Pt, Ge, and Si. The phase diagrams of these elements, i.e., temperature T versus pressure p, have been thoroughly studied and described in detail in references such as (https: / / doi.org / 10.1016 / j.jpcs.2015.05.006.) based on high-precision experimental techniques and modern computational analysis methods. The melting curves of the selected elements are shown in [reference needed]. Figure 2 It serves as the calibration basis for establishing the load characteristic curve of a high-pressure device under high-temperature conditions.

[0063] The pressure sensor comprises a metal or semiconductor calibration element, which is a wire resistor with a cross-sectional area S = 0.7–0.8 mm² and a length of 3–5 mm, connected to the lead-out electrical contacts of the measuring circuit for determining the phase transition temperature using a thermocouple. Wire resistors made of Cd, Pb, Al, Ag, Cu, Au, Ni, Fe, Pd, Pt, Ge, or Si are connected in parallel in a DC circuit. Within a pressure range of 1–10 GPa, the melting temperature T is recorded by changes in the sensor signal pattern. 熔 The change in sensor signal is caused by the change in the geometry of the calibration element and its dissipation during the melting process, which leads to the disconnection of the circuit link and the cessation of the working current.

[0064] Step 3. Introduce multiple insulating electrical contacts into the synthesis chamber of the experimental high-voltage device. The calibration element is connected to the insulating electrical contacts respectively and is used for resistance heating, measurement of thermoelectric potential and conversion of the calibration element.

[0065] To perform the measurement process and ensure resistance heating, six insulating electrical contacts were introduced into the experimental high-pressure device working unit, namely the synthesis chamber. Two of these contacts were used to achieve resistance heating, two were used to measure the thermoelectric potential of the thermocouple, and the remaining two insulating electrical contacts were used to determine the melting process of the selected calibration material (i.e., the transition of the marker from a solid to a liquid state). The specific pressure point was then deduced from the melting point.

[0066] In cases where a six-sided high-voltage device is used to compress the working unit, the aforementioned six insulated electrical contact leads are connected to a hard alloy pressure anvil for easy operation.

[0067] Step 4. Place the thermocouple within the working volume of the high-pressure device, and ensure that the hot junction of the thermocouple is located near the calibration element of the pressure sensor.

[0068] To determine the melting temperature experimentally, Pt-PtRh (pure platinum and platinum-rhodium alloy) thermocouples were specified. These Pt-PtRh thermocouples were directly introduced into the working volume of the high-pressure device's synthesis chamber, and contact with the measuring instrument (FX1000 paperless recorder) was ensured by two hard alloy anvils from a six-sided press, facilitating signal measurement. The hot junction of the thermocouple should be located close to the marked position (minimum distance 0.2 mm, maximum distance 2.5 mm) to balance measurement efficiency and accuracy.

[0069] Step 5. The pressure sensor is equipped with at least two calibration elements as wire resistors, which are connected in parallel.

[0070] The pressure sensor includes two or more markers, or calibration elements, arranged in the same plane and isolated from the plane containing the thermocouple hot junction by a 0.2 mm thick insulating layer, ensuring accurate signal measurement. The pressure sensor consists of 2–5 markers connected in parallel as wire resistors, connected to two conductive leads in the assembled state, and in contact with two hard alloy pressing anvils, ensuring that the two measurement signals are mutually insulated.

[0071] Step 6. Measure the pressure when the calibration element melts using a pressure sensor, as well as the corresponding melting temperature, and establish a functional relationship between the pressure and temperature inside the synthesis chamber by fitting.

[0072] To determine the pressure-temperature relationship ∆p=f(T) and establish the load characteristics of a quasi-static high-pressure device when the compressor pressure is increased, the pressure sensor structure should be able to measure at least two points, p1 and p2, and their corresponding temperatures using pressure measurement markers. These points can be used to establish the functional relationship. The design of this sensor structure should specify the introduction of at least six insulated electrical input terminals into the cavity of the high-pressure device, using insulated contact: each pair should be individually connected to the resistance heating system of the working unit, the thermocouple, and the calibration element of the pressure sensor. According to the above specifications, the minimum number of markers for the calibration element should be no less than two, and ideally more—three, four, or more, depending on the span of the temperature measurement range.

[0073] The solution to this problem, which involves using multiple markers to obtain p,T data during a single press loading cycle and connecting the sensor to an FX1000 paperless recorder via a channel with two electrical inputs, takes into account the following key factors that determine the operation of the pressure sensor:

[0074] Markers, or calibration elements ( Figure 2 The sample is designed as a linear object with an equivalent diameter not exceeding 0.3 mm and a length of 4–5 mm. The metallic marker is a parallelepiped with a corresponding cross-section. Larger equivalent diameters will result in less pronounced variations, which is detrimental to measurement.

[0075] Experiments show that when melting occurs under quasi-hydrostatic compression conditions in NaCl or CsCl plastic media, the melting temperature T corresponding to each marker is reached. 熔 When this type of sample is used, it loses its original shape and spreads out as droplets with a diameter of 0.1–0.5 mm. If such a sample is used as a resistor and a constant current is passed through it, the current will not be able to continue passing through the marker due to the interruption of the solid medium's continuity, and therefore the resistor will stop working.

[0076] Resistors with different resistance values ​​R1 and R2 and different melting temperatures T1 and T2 are connected to a DC power supply, such as... Figure 3 As shown, a DC power supply 1 with voltage U provides a current I in the circuit. The value of current I is equal to U / R, where U is the voltage of the DC power supply, and the total resistance R is calculated according to the known relationship for this type of conductor electrical connection:

[0077] ;

[0078] When the marker resistor R1 melts and its circuit breaks, we can assume that R1 → ∞, 1 / R1 → 0, and therefore 1 / R > 1 / R2, meaning the total resistance R is less than the value of the marker resistor R1 before it melts. Consequently, the current I in the circuit will increase abruptly. For the parallel connection of resistors R1 and R2, recording this sudden change in current I allows us to determine the lower melting temperature T. 熔 The melting temperature of the resistor R1 of the calibration element. Figure 3 The markers-calibration elements R1 and R2 with melting temperatures of T1 and T2 are connected in parallel, where T1 < T2.

[0079] Therefore, in a circuit with parallel-connected markers—resistors R1 and R2—a step increase in the recorded current allows determination of the melting temperature of the calibrator R1. It is obvious and readily apparent that in a parallel circuit ( Figure 3 In this method, when the number of resistor-markers is increased to two or more, and they have different melting temperatures, the current jump at the melting of each marker can be recorded, and the corresponding melting temperature T can be determined. 熔 In order to fit the data points more accurately.

[0080] Implementing the inventive principle described in steps 1-6 enables the measurement of the pressure of the hydrostatic high-pressure device when the temperature of the synthesis chamber is increased to 1800–2000 ℃. Once the externally applied oil pressure and the pressure of the synthesis chamber are determined, and their load characteristics, i.e. the function curve of the oil pressure of the six-sided press and the pressure of the synthesis chamber, are established, they can be used to guide production.

[0081] Example 2

[0082] A device for accurately measuring the internal pressure of a high-pressure chamber at high temperatures includes a pyrophyllite synthetic block. For the experiment, a standard six-sided press with a pressure head diameter of 420 mm was used, along with a cubic container 1 made of pyrophyllite, measuring 43.5 × 43.5 × 43.5 mm. The container 1 has a 27 mm diameter hole for placing the synthetic chamber 9. Figure 4 As shown.

[0083] Heating of the synthesis chamber 9 is achieved through upper and lower pressure anvils, with a working surface size of 31 mm, using conductive graphite tubes 6. An insulation tube 7 is installed within the pyrophyllite synthesis block (block 1) containing heating elements. Conductive graphite sheets 5 are located at both ends of the insulation tube 7, and dolomite columns 4 for pressure transmission are located at both ends of the conductive graphite sheets 5. Conductive steel caps 3 are located on the outside of the dolomite columns 4, and stone rings 2, made of pyrophyllite, are located on the outside of the steel caps 3, providing a sealing function under high pressure. The conductive graphite tube 6 is installed inside the insulation tube 7, and its interior is filled with a quasi-static medium (hexagonal boron nitride h-BN). The synthesis chamber 9, containing the quasi-static medium, is located within the graphite tube 6. A position for placing a high-pressure sensor is selected in the central area of ​​the synthesis chamber 9. Figure 4 Area 8 is where the pressure sensor is placed. See the schematic diagram of the pressure sensor structure. Figure 5-7 As shown. The quasi-static water medium in which the pressure sensor is placed within the synthesis chamber 9 is high-purity crystalline hexagonal boron nitride (h-BN).

[0084] like Figure 5 As shown, the pressure sensor includes a disc-shaped housing 11 with a diameter of 18.4 mm and a height of 1 mm (h-BN), serving as the carrier of the calibration element. Two symmetrically distributed holes with a diameter of 5 mm are machined into the housing 11. These holes are used to house electrical contact graphite sheets 14 as contact bodies. The electrical contact graphite sheets 14 are graphite discs that serve as connections between signal wires and the calibration element. The calibration element 13 connects the two electrical contacts 14 to form a parallel circuit, constituting a measurement system for measuring the circuit resistance of the selected calibration element. This records the melting and determines the TP relationship corresponding to these effects. Figure 2 The curve in the image.

[0085] The two calibration elements 13 are connected in parallel. Figure 3 The corresponding contact terminals of calibration element 13 are interconnected by connecting to two electrical contact graphite sheets 14, which are connected to two signal wires 15 made of molybdenum. Figure 5 The signal wire is electrically connected to the center of the electrical contact 14 and further connected to the pressure anvil of the high-voltage device for signal output.

[0086] The lower part of the housing 11 of the pressure sensor is in contact with the platinum-rhodium thermocouple PtRh(30)-PtRh(6), i.e., thermocouple junction 12. The hot end of the thermocouple junction 12 is located at the center of the working unit synthesis cavity 9. Figure 5Thermocouple signal wire 16 is led out through a hole drilled in the pyrophyllite block 1 and directly contacts the pressure working surface of the hard alloy anvil. For temperature and pressure measurements, thermocouple signal wire 16 is kept as close as possible to the calibration element 13 but not in contact. Thermocouple contact 12 is used to measure the electromotive force, and then the temperature inside the cavity is determined according to the thermocouple electromotive force versus temperature correspondence table. The pressure sensor operates by measuring the temperature using a thermocouple connected to the two output terminals of the calibration element 13. The temperature of the synthesis cavity 9 is indirectly determined by measuring the electromotive force of the thermocouple, and the pressure of the synthesis cavity is indirectly determined by measuring the resistance change of the calibration element 13.

[0087] Melting temperature T of marker in parallel circuit 熔 Recording is achieved through two connections to the paperless recorder, i.e., direct measurement via the measuring device. Therefore, according to the invention, four independent electrical input terminals must be provided to ensure the proper functioning of the pressure sensor. For a six-sided press, these electrical input terminals can be implemented using a lateral compression plunger with a carbide pressure anvil, while ensuring the necessary electrical insulation.

[0088] It is important to emphasize that by employing a pressure sensor structure, compressing the container to 3 GPa at room temperature ensures that the minimum distance between the thermocouple junction 12 and the wire standard, i.e., the calibration element 13, is 0.2-0.35 mm. This should be sufficient to characterize the melting temperature T. 熔 High-precision measurement.

[0089] Figure 5-7 The pressure sensor structure shown can obtain two coordinate points p1, T1 and p2, T2 on the T,p graph by arranging two filamentary calibration elements 13, and can determine the pressure change from p1 to p2 within the temperature range T1-T2.

[0090] The number of filamentary calibration elements 13 can be greater than two—the size of the graphite electrical contacts allows for the arrangement of three or more resistive elements within the sensor housing to record the melting process (if such a requirement exists). In practice, to evaluate the compressibility of the high-pressure device and the actual pressure value, two to three pressure values ​​are usually sufficient when constructing the load characteristic curve.

[0091] Using data from known element melting curves in the literature (see...) Figure 2 ( ), an initial standard-calibration element 13 combination can be selected to determine the load characteristics of the high-voltage device. For the temperature range T = 500–1400 ℃, phase state T,p diagrams of Cd, Pb, Ge, Si, Al, Ag, Au and Cu can be used.

[0092] Based on the highest temperature achievable in the working volume of the compressed quasi-static medium, a pressure sensor containing two or three standard calibration elements can be used. In the high-temperature region, when the temperature T is greater than 1400–1500 ℃, a parallel resistive element made of Fe, Ni, Pd, and Pt can be used.

[0093] Example 3

[0094] A method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures is provided. An example of this method is used in a 6×20 MN high-pressure device with a 420 mm anvil diameter to illustrate its application in constructing load characteristic curves of a high-pressure device under high-temperature conditions.

[0095] Using container 1 and synthesis chamber 9 (see...) Figure 4 Under these conditions, the loading characteristic curves (p, T) at room temperature were determined based on the known fixed points of bismuth, thallium, and barium, see [reference needed]. Figure 8 . Figure 8 The lower curve in the figure is constructed based on the resistance measurement data of Bi, Tl and Ba during the pressure increase process at room temperature. The corresponding fixed pressure points are 2.54 GPa, 3.67 GPa and 5.50 GPa, respectively. The pressure p=f(Q) relationship curve is established, where Q represents the top press oil pressure. Figure 8 The upper curve in the figure is achieved using the proposed pressure sensor (see...). Figure 5 The p=f(Q) relationship curve under working block heating conditions was obtained by measuring the melting temperature of selected standard-calibrator samples to determine the load characteristics of the high-pressure device. This curve was established using pressure sensors containing two calibrators (Ag-Cu) and three calibrators (Al-Ag-Cu). Figure 8 It can be seen that the data from traditional room temperature pressure tests deviate significantly from the actual pressure data at high temperatures.

[0096] Ag-Cu and Al-Ag-Cu calibration elements are used as the working elements, connected in parallel and integrated into the measurement circuit. These working elements are made of high-purity metal (99.99%) wire with a diameter of 0.3 mm and a working length of 5–7 mm. For Ag-Cu and Al-Ag-Cu, the pressure sensor contains 2 and 3 filamentary resistive elements, respectively (see...). Figure 5 These calibration elements reliably contact the electrical contact graphite sheets, or contact bodies, of the four signal wires, thereby ensuring the effectiveness of the proposed sensor (see [link to sensor]). Figure 5 The measurement is implemented.

[0097] Measurements using Ag-Cu and Al-Ag-Cu sensors are performed in two separate cycles, with the loading conditions of the top press and the heating conditions of the synthesis chamber 19 kept consistent. The loading and heating cycles of the working volume proceed as follows:

[0098] Stage I: A press with a diameter of 420 mm is first loaded until the compression gasket is formed, and then loading is continued at a rate of 2–2.2 MN / min until a load of Q = 10–12 MN is reached, so as to pressurize the synthesis chamber.

[0099] Stage II: Under the condition that the top press load Q=10–12 MN, the heating of the pyrophyllite synthesis block 1 is started to ensure that the current power increase rate is 0.5–1.0 kW / min, while the pressurization speed of the top press is reduced to 0.6–0.9 MN / min to realize heating.

[0100] Stage III: The recording of the melting effect of the calibrated metal in the Ag-Cu and Al-Ag-Cu measurement synthesis blocks is completed, and the pressure at the time of fusing is determined.

[0101] For the synthesis block containing two calibrated metals, the thermocouple reading is recorded when Ag melts - in the current record through the pressure sensor, the melting effect appears as a jump caused by the disconnection of the Ag calibrated metal circuit, as shown in Figure 9 a. As the temperature further rises and Cu melts, the current stops passing through the pressure sensor due to the circuit disconnection. The temperature at which the current stops passing (I=0) corresponds to the melting effect of Cu, as shown in Figure 9 a.

[0102] For the Al-Ag-Cu sensor, the recording method of the melting effect of the three calibrated resistors Al-Ag-Cu is similar to that of the Ag-Cu sensor. Figure 9 is a functional relationship diagram between oil pressure and chamber pressure obtained by using two calibrated metals and three calibrated metals respectively. When Al and Ag melt, only jumps corresponding to the melting temperatures of Al and Ag are observed in the sensor record, as shown in Figure 9 b; when the temperature continues to rise thereafter, the melting of Cu can be determined by the moment when the current stops passing, as shown in Figure 9 b. Figure 9 In the figure, circle 1 is the current jump when the first calibrated body (Ag) melts, where the melting point is relatively low, case a corresponds to the temperature , case b corresponds to the temperature , ; circle 2 is the point where the copper current stops passing, and both case a and case b correspond to the temperature .

[0103] Example 4

[0104] A method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures. This invention is used to determine the compressibility of a quasi-static medium and the pressure level of a high-pressure device (AVD) under heating conditions. The following operations need to be performed:

[0105] according to Figure 4 Prepare and assemble the working synthesis cavity according to the scheme shown;

[0106] according to Figure 5-7 The scheme shown involves preparing, assembling, and arranging pressure sensors in the working area. The pressure sensors can consist of two or three calibration metals, i.e., calibration elements, and are connected to the measurement circuit as parallel resistors. PtRh thermocouples (type B, diameter 0.25 mm) are used.

[0107] The container equipped with the pressure sensor is placed in the high-pressure press system, and the four leads of the pressure sensor, including the calibration element signal wire 15 and the thermocouple signal wire 16, are connected to the four lateral anvils of the top press by preloading the hydraulic system and moving the clamping element accordingly.

[0108] As described above, the container equipped with the synthesis chamber and pressure sensor is loaded (compressed) and measured to obtain load characteristic data, which facilitates subsequent data fitting and enables control of oil pressure in diamond production.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for accurately measuring the internal pressure of a high-pressure cavity at high temperatures, characterized in that, Includes the following steps: Step 1. Set the temperature and pressure ranges for measurement; Step 2. Select at least two metals as calibration elements for the pressure sensor and fabricate them into wire resistors. Determine the melting temperature of the calibration elements based on their temperature-pressure curves. Step 3. Introduce multiple insulating electrical contacts into the synthesis chamber of the high-voltage device. The insulating electrical contacts are connected to the calibration element and the thermocouple, respectively. Step 4. Bring the hot junction of the thermocouple close to the calibration element of the pressure sensor; Step 5. At least two wire resistors on the pressure sensor are connected in parallel and placed in the quasi-static water medium of the synthesis chamber of the high-pressure device; Step 6. Based on the melting temperature of the calibration element when it melts, determine the pressure of the calibration element when it melts using the temperature-pressure curve of the calibration element, and establish a functional relationship between the pressure and temperature inside the synthesis chamber by fitting; determine the pressure of the quasi-static medium inside the synthesis chamber at the corresponding temperature through the functional relationship.

2. The method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 1, characterized in that, The temperature range is 500–2000℃, and the pressure range is 1–10 GPa. Within the synthesis chamber of the high-pressure device, the current jump is recorded when each calibration element melts, and the corresponding melting temperature T is determined. 熔 The pressure at which melting occurs is determined based on the temperature-pressure curve of the calibration element; the melting temperature T is measured using at least two calibration elements. 熔 The corresponding pressure was fitted to establish the functional relationship between the internal pressure and temperature of the synthesis chamber.

3. The method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 2, characterized in that, The metal is at least two of the following: Cd, Pb, Al, Ag, Cu, Au, Ni, Fe, Pd, Pt, Ge, and Si. For a temperature range of 500–1400℃, the phase temperatures and pressures of Cd, Pb, Ge, Si, Al, Ag, Au, and Cu are used to determine the temperature-pressure curves in step 2; When the temperature is greater than 1400–1500℃, the pressure of the quasi-static medium is measured using a parallel wire resistor made of at least two of Fe, Ni, Pd or Pt.

4. The method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 2 or 3, characterized in that, The filament resistor has a cross-sectional area of ​​0.7–0.8 mm² and a length of 3–5 mm; The distance between the hot junction of the thermocouple and the calibration element is 0.2 mm to 2.5 mm; At least two calibration elements are arranged in the same plane and isolated from the plane containing the hot junction of the thermocouple by an insulating layer.

5. The method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 4, characterized in that, The number of insulating electrical contacts is provided in multiples, including insulating electrical contacts for heating the filament resistor, insulating electrical contacts for measuring temperature by measuring the thermoelectric potential of the thermocouple, and insulating electrical contacts for determining the melting process of the calibration element from solid to liquid; the leads of the multiple insulating electrical contacts are connected by a hard alloy pressing anvil. The thermocouple is a Pt-PtRh thermocouple, which is directly introduced into the working volume of the synthesis chamber of the high-pressure device.

6. The method for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 5, characterized in that, The signal change on the filament resistor is caused by the change in geometry and the dissipation that occurs during melting, which leads to the circuit being broken and the operating current stopping. When melting occurs under quasi-hydrostatic compression conditions in NaCl or CsCl plastic media, the melting temperature T corresponding to each calibration element is reached. 熔 When this happens, the filament resistor loses its original shape and spreads out in the form of droplets with a diameter of 0.1–0.5 mm.

7. A device for accurately measuring the internal pressure of a high-pressure cavity at high temperature, utilizing the method for accurately measuring the internal pressure of a high-pressure cavity at high temperature as described in any one of claims 1-6, characterized in that... The assembly includes a synthesis block (1), which is equipped with a heat insulation tube (7), which is equipped with a conductive graphite tube (6), and conductive graphite sheets (5) are provided at both ends of the conductive graphite tube (6); the conductive graphite tube (6) is filled with a quasi-static water medium, and a pressure sensor is provided in the placement area (8) in the middle of the synthesis chamber (9). The pressure sensor includes a housing (11), on which two symmetrical electrical contact graphite sheets (14) are provided, and two parallel calibration elements (13) are provided between the two electrical contact graphite sheets (14).

8. The device for accurately measuring the internal pressure of a high-pressure cavity at high temperatures according to claim 7, characterized in that, The housing (11) has two symmetrically distributed holes, and electrical contact graphite sheets (14) are provided on the holes. The two electrical contact graphite sheets (14) are connected by at least two parallel calibration elements (13). The electrical contact graphite sheets (14) are provided with calibration element signal wires (15). The lower part of the housing (11) is in contact with the thermocouple junction (12), and the thermocouple junction (12) is connected to the thermocouple signal wire (16). The calibration element signal wire (15) and the thermocouple signal wire (16) are in contact with the working surface of the hard alloy pressure anvil.

9. The device for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 7, characterized in that, The conductive graphite sheet (5) has stone pillars (4) for pressure transmission at both ends. The outer side of the stone pillars (4) has a steel cap (3) for conducting electricity. The steel cap (3) is sealed to the composite block (1) through a stone ring (2). The minimum distance between the thermocouple junction (12) and the calibration element (13) is 0.2-0.35 mm.

10. The device for accurately measuring the internal pressure of a high-pressure cavity at high temperature according to claim 7, characterized in that, The quasi-static water medium is hexagonal boron nitride h-BN; The shell (11) is disc-shaped; At least two of the calibration elements (13) have their corresponding contact ends disposed on an electrical contact graphite sheet (14), and the calibration element signal wire (15) is electrically connected to the center of the electrical contact graphite sheet (14); The thermocouple junction (12) is located at the center of the lower part of the housing (11) and between the calibration elements (13).

Images